head to head
Neither is simply harder - they are hard in different places. Beyond Good & Evil demands more optimization; Grand Theft Auto V demands more reads.

Optimization · Practiced Mastery
Action-adventure about a photojournalist exposing an alien conspiracy with stealth and a camera.

Execution · Practiced Mastery
Sandbox crime playground spanning shooting, driving, and a persistent online economy.
Beyond Good & Evil leans Optimization (Practiced Mastery); Grand Theft Auto V leans Execution (Practiced Mastery).
Grand Theft Auto V leans a little harder on execution, though the gap is small.
Beyond Good & Evil
Light combat, stealth timing, and hovercraft racing
Grand Theft Auto V
Driving and shooting demand decent inputs.
Grand Theft Auto V leans clearly harder on reads.
Beyond Good & Evil
Guards follow fixed patrol scripts
Grand Theft Auto V
Online PvP exists but mostly gear/positioning, not modeling.
Same score on variance - which means the number cannot separate them. The difference is in what each one asks of you.
Beyond Good & Evil
First-run photo hunts and story beats
Grand Theft Auto V
Some mission and lobby randomness.
Beyond Good & Evil leans clearly harder on optimization.
Beyond Good & Evil
Stealth routes, pearls economy, and puzzles
Grand Theft Auto V
Heists, money loops, builds learnable.
A matching score does not mean a matching test. Two games can both sit at 10 on execution and demand completely different things of you - which is why the reasoning above matters more than the number beside it.